1. Field of the Invention
The present invention relates to a gas sensor.
2. Description of the Related Art
A gas sensor that detects the concentration of predetermined gas, such as NOx or oxygen, in gas to be measured such as exhaust gas of a motor vehicle has been known. Such a gas sensor may be cracked since, for example, water generated when an engine starts is deposited onto a sensor element and, thus, the temperature of the sensor element drops. To prevent such an issue, a technique to attach a protection cover to cover the sensor element is proposed. For example, PTL 1 describes a gas sensor having a double structure protection cover provided on the outer periphery of the tip end portion of the sensor element. The protection cover has a vent hole for leading exhaust gas to the inside.